1. Characterization of He implanted Eurofer97
Inês Carvalho, Henk Schut, Alexander Fedorov,
Natalia Luzginova, Pierre Desgardin, Jilt Sietsma
Edinburgh, 4-5 June 2013

2. Outline Project overview Techniques Experimental details Results
Positron annihilation
Thermal desorption spectroscopy
Experimental details
Results
Helium implantations keV and 2 MeV
Helium release mechanisms
Example: 500 keV, He/cm2
Overall picture
Final remarks & Future Work

3. Project Overview Eurofer97 (Fe - 9Cr - 1W - 0.2V - 0.1Ta - 0.1C wt.%)
Correlation of microstructure and mechanical properties
Understanding structural defects that affect the mechanical properties
Evolution of defect structures formed due to clustering and coalescence of POINT DEFECTS
Helium-vacancy clusters
Helium-filled bubbles
Interstitial loops
Thermal desorption spectroscopy (TDS)
defect populations
thermal stabilities of defects
Positron annihilation
thermal evolution of free-volume related defects
Electron Microscopy
microstructure of ion implanted and (neutron) irradiated samples

4. Project Overview
Use of thermal desorption spectroscopy (TDS) and electron microscopy on Eurofer97 neutron irradiated material
First approach: reproduction of neutron irradiation conditions
He implantation with 500 keV and 2 MeV energies
Study of defect structures by positron annihilation and Thermal Desorption Spectroscopy (TDS)
After: comparison of results – He implanted vs. neutron irradiated samples
Reference Material
Study of pre-existing defects
Ion Implantation (He)
Simulation of neutron irradiation defects
Neutron Irradiation
Real irradiation conditions
now

5. Techniques

6. Techniques – VEP Positron annihilation 𝑬=𝟓𝟏𝟏 𝒌𝒆𝑽± 𝒄 𝒑 ∕∕ 𝟐
Variable energy positron beam (VEP)
22Na source
Energy up to 25 keV (~ 1µm depth for Fe)
Thermalization followed by trapping and annihilation
Emission of 2𝛾 of 511 keV
Lifetime of ~ 200 ps
𝑝 𝑣𝑎𝑙𝑒𝑛𝑐𝑒 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠 ≪ 𝑝 𝑐𝑜𝑟𝑒 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠
W parameter  core electrons
S parameter  free electrons
 vacancies,
dislocations,
free volumes
𝑬=𝟓𝟏𝟏 𝒌𝒆𝑽± 𝒄 𝒑 ∕∕ 𝟐

7. Techniques – VEP Positron annihilation 𝑬=𝟓𝟏𝟏 𝒌𝒆𝑽± 𝒄 𝒑 ∕∕ 𝟐
Variable energy positron beam (VEP)
22Na source
Energy up to 25 keV (~ 1µm depth for Fe)
Thermalization followed by trapping and annihilation
Emission of 2𝛾 of 511 keV
Lifetime of ~ 200 ps
𝑝 𝑣𝑎𝑙𝑒𝑛𝑐𝑒 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠 ≪ 𝑝 𝑐𝑜𝑟𝑒 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠
W parameter  core electrons
S parameter  free electrons
 vacancies,
dislocations,
free volumes
𝑬=𝟓𝟏𝟏 𝒌𝒆𝑽± 𝒄 𝒑 ∕∕ 𝟐

8. Techniques - TDS Thermal desorption spectroscopy
Heating rate of 0,33 K/sec
Ramp anneal from 300 K up to 1500 K
Ultra high vaccum
Temperature of released helium related to the type of trap and thermal stability (He-defect binding energy)
Amount of He released associated with defect concentration

9. Experimental details

10. Experimental TDS PA Energy 500 keV 2 MeV Doses (He/cm2) 1 x 1014-1017
Eurofer97 - Fe-9Cr-1W-0.2V-0.1Ta-0.1C (wt.%)
Tempered martensitic structure
Ion beam Helium implantation (RT)
Sample size: 1.2 x 1.2 x 0.05 cm2
Measurements
Positron annihilation DB
TDS + in situ DB annealing
Energy
500 keV
2 MeV
Doses (He/cm2)
1 x
Current (nA)
270 – 280
Time (h)
1 - 15
Dpa
0.08 – 0.8
0.07 – 0.7
Ion range (µm)
~ 1
~ 3
Positron range
Schematics of implanted sample PA
TDS
TRIM calculation for 1 x 1015 He/cm2

11. Experimental Techniques
Thermal desorption spectroscopy
Annealing from 300 K to 1500 K
Heating rate of 0.33 K/sec
Vacuum of Torr
Positron Beam Doppler Broadening
In situ annealing with similar annealing rate to TDS
Annealing duration of 5 min
Oven cooling
Measurement at room temperature

12. Results He implantations 500 keV & 2 MeV RT, 1014-1017 He/cm2

13. Implantation Current (µA)
VEP 500 keV and 2 MeV, He/cm2
Positron range
Implantation Current (µA)
Dose (He/cm2)
500 keV
2 MeV
1014
0.12
0.31
1015
0.28
1016
0.27
0.21
1017
1.63
2.56

14. VEP - 500 keV and 2 MeV, 1014-17 He/cm2 Annealing study 500 keV
Increase of S parameter with increasing dose  Dose effect !!!
Similar behaviour not only within same implantation energy but also comparing both energies
500 keV
VEP – decrease of S for 1017 He/cm2
Not observed in annealing study

15. TDS – 500 keV & 2 MeV Helium release

16. TDS – 500 keV & 2 MeV retention: 25-80% retention: 75-110%

17. Interpretation of results Example: 500 KeV, 1016 He/cm2
Overnight
bake out
Below 300 K
Interstitial He is mobile below RT
300 K
HELIUM IMPLANTATION

18. Interpretation of results 500 KeV, 1016 He/cm2
He in substitutional position
Vacancy assisted diffusion of He
Annealing of vacancies and vacancies clusters
1 µm

19. Interpretation of results 500 KeV, 1016 He/cm2
Dissociation of overpressured HenVm (n < m) clusters
Possible re-trapping of He
Formation of bigger clusters
Stability of S level mainly due to HeV and stable HenVm pairs
1 µm

20. Interpretation of results 500 KeV, 1016 He/cm2
Ostwald ripening – formation of bubbles
Increase of S for deeper implantation region
Smaller diffusion length of He before retraping
Dissociation of HeV pairs
Phase transition of Eurofer97 (1160 K)
1 µm

21. Interpretation of results 500 KeV, 1016 He/cm2
Release of He from bubbles
Dissociation vs. Migration mechanism
1 µm

22. Interpretation of results Overall picture

23. Final remarks
Higher implantation dose leads to an increase in the S parameter
Also observed in the positron annealing study
Repetition of implantation 500 keV, 1017 He/cm2 necessary
Similar TDS spectra shape for all doses
Increasing He release up to 1500 K
Phase transition/HeV dissociation in the range 1100 – 1200 K
Peak on the left of the phase transition peak
Helium release mechanisms are identified

24. Future work Continuation of He implantations Desorption experiments
He implanted samples
Neutron irradiated samples
TEM
Correlation of microstructure and mechanical properties